An extensive preliminary patentability search was not conducted with respect to the instant invention. The following United States Patents, however, are believed representative of the art which existed prior to this invention: Nos. 3,646,794 Tishken; 3,653,245 Tishken; 3,928,998 Torres; 3,948,013 Lobaugh; and 3,996,780 German. These patents disclose various kinds of serrated shapes. In all instances, however, this prior art formed the serrations by cold working.
The Tishken patents, see especially '245 at FIG. 6 and column 3, line 58 to column 4, line 5, employ generally trapezoid-shaped teeth to form notches in strips of grating workstock by cold rolling. Torres teaches the use of a pair of channeled rollers having in their bottom walls pluralities of holes having cap-shaped bottom portions, see FIGS. 5b and 13 along with the passage from line 56 of column 6 through line 11 of column 7. Lobaugh is of interest in its teaching of how to form a grating using bars, see FIG. 3, although it is silent as to how the bar itself is produced. Finally, the German patent, see FIG. 5 and column 3 at lines 30 to 44 along with column 5 at line 26 through column 6 at line 15, shows the use of a pair of grooved rolls, one of them being provided with teeth, to impart notches to an edge of a strip, all of this being done by cold working of the steel.
There are obvious problems associated with cold working. These include the difficulity of maintaining the bars straight both before and after forming the notches, the difficulity of preventing bulging of the bars as caused by cold working on a narrow edge, the slow speeds involved, the large energy requirements and the cost of the equipment.